1. Field of the Invention
The present invention relates to an oscillator applied to a control circuit of a power converter and a control method thereof, and particularly to an oscillator and a control method thereof that can control a frequency of a gate control signal to be varied with a compensation voltage when a load is middle or heavy.
2. Description of the Prior Art
A control circuit applied to a power converter provided by the prior art can output a pulse width modulation signal to a power switch of a primary side of the power converter in pulse width modulation mode, wherein a frequency of the pulse width modulation signal is a first fixed value when a compensation voltage corresponding to a load coupled to a secondary side of the power converter is less than a first predetermined voltage, is varied with the compensation voltage when the compensation voltage is between the first predetermined voltage and a second predetermined voltage, and is a second fixed value when the compensation voltage is greater than the second predetermined voltage. When the compensation voltage is greater than the second predetermined voltage, the load is middle or heavy, but the frequency of the pulse width modulation signal is the second fixed value, the prior art has disadvantages as follows when the compensation voltage is greater than the second predetermined voltage: first, a response of an output voltage of the secondary side of the power converter corresponding to the load is poorer; second, ripples of the output voltage cannot be suppressed; third, conversion efficiency of the power converter cannot be increased.